1. Field of the Invention
The present invention relates to a control system for a motor vehicle having a continuously variable transmission.
2. Description of the Prior Art
There have heretofore been known control techniques wherein, in order to suppress any of undesirable various phenomena ascribable to the combustion of fuel in an internal combustion engine, for example, the occurrence of knocking and the increase of Nox concentration, the ignition timing of the engine is retarded (an advance angle correction amount is corrected to the retardation angle side).
Japanese Patent Application Laid-open No. 180368 /1990 discloses a technique wherein, in case of the occurrence of knocking in a motor vehicle having a continuously variable transmission (abbreviated to "CVT"), the knocking is suppressed by raising the target r.p.m. of an engine when the motor vehicle is in a constant speed drive state, and by heightening the gear shift speed of the CVT when the motor vehicle is in a rapid acceleration state. Japanese Patent Application Laid-open No. 200034/1986 discloses a technique wherein the knocking is extinguished in such a way that, upon the occurrence of knocking, a knock detection signal from a knock sensor is entered into a control unit, by which the change gear ratio of a CVT is decreased.
In the prior-art control for preventing the knocking from occurring or for preventing NOx production from increasing, as understood from the known examples stated above, only the retardation angle correction of the ignition timing, or only the gear shift speed or change gear ratio of the CVT installed in the motor vehicle has been paid attention. In other words, only one of the factors has been dealt with independently as the countermeasure of above problems.
The situation is grounded on the fact that the developments of automobiles in recent years cannot avoid being specialized due to the high technical levels thereof, so the control of the retardation angle as the countermeasure on the engine development side and the control of the gear shift speed or the change gear ratio as the countermeasure on the CVT development side are difficult to be merged with each other.
However, this fact conversely signifies that, even if a certain motor vehicle is assumed to have both a countermeasure based on the retardation angle control and a countermeasure based on the CVT control by way of example, in order to prevent the knocking and to prevent the NOx increase, the controls will be executed independently of each other.
The fuel consumption of the internal combustion engine, however, worsens depending upon the operating states thereof. More specifically, the fuel consumption worsens less when the retardation angle correction of the ignition timing is adopted in some cases, whereas it worsens less when the increase correction of the target r.p.m. of the CVT is adopted in the other cases. Accordingly, when the prior-art techniques are merely combined with the intention of suppressing the knocking or the NOx increase, the problem is apprehended that an appropriate control with the fuel consumption taken into consideration will not be executed, so the fuel consumption will worsen excessively.